Carbon dioxide biomass respiration

Figure 3.2 Summary of decay or organic matter (residue) and accompanying synthesis of decomposer biomass and accumulation of carbon dioxide due to microbial respiration.

As organisms feed, they convert some organic matter and nutrients into biomass of their own bodies, while another portion is excreted as waste from respiration. Therefore, as food chains proceed toward completion, the amount of biomass may be totally reduced through metabolic processes to carbon dioxide, water, and several mineral nutrients that remain in solution. 

The substrate-indnced respiration (SIR) method was developed as a rapid means of estimating microbial activities in soils (Beare et al., 1990 Neely et al., 1991). The use of selective inhibitors such as streptomycin for bacteria and cycloheximide for fungi, in conjunction with substrate additions, has been used to quantify bacterial and fungal contributions to the total metabolism of microbial decomposers. The SIR procedure involves addition of a labile carbon source (e.g., glucose or acetate) to provide a carbon nonlimiting condition. The short-term increase in carbon dioxide production is proportional to the active microbial biomass and activity. The concept of addition of labile carbon to determine the kinetics of substrate utilization by microorganisms has been extensively studied in various ecosystems including wetlands and aquatic systems. 

Carbon Dioxide - A colorless, odorless noncombustible gas with the formula C02 that is present in the atmosphere. It is formed by the combustion of carbon and carbon compounds (such as fossil fuels and biomass), by respiration, which is a slow combustion in animals and plants, and by the gradual oxidation of organic matter in the soil. 

Secondary consumers eat the primary consumers and produce feces waste, biomass, and cellular respiratory products. Respiration totally degrades the biomass, usually producing water and carbon dioxide. These compounds cannot be further exploited for their energy values and so are the ultimate energy sink for an ecosystem. 

The atmosphere is a source of essential raw materials, both for organisms and for industrial use, and has major applications in the practice of green chemistry. Plants that provide the foundation of food chains within which all organisms thrive extract the carbon dioxide that they use to build biomass from the atmosphere. Animals and other organisms that perform oxic respiration obtain the molecular O2 they require from the atmosphere. The refractory N2 in the atmosphere is converted to biomass and protein nitrogen by bacteria growing in soil and water. 

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